This invention relates generally to improved dwell and depth attachments for power drills and the like. More particularly, but not by way of limitation, this invention relates to an improved dwell and depth attachment for power drills and the like that includes means for precisely maintaining the desired depth to be drilled.
A number of attempts have been made in the past to accurately control the depth of a drilled hole as measured from the surface of the material in which the hole is drilled. While it can be accomplished manually by carefully drilling each hole, it becomes a more difficult problem when high accuracy and repeatability are to be accomplished in relatively high production situations. Attempts to provide apparatus for controlling the depth are illustrated by U.S. Pat. No. 3,767,313 issued Oct. 23, 1973 to Luis A. Bohoroquez et al. and U.S. Pat. No. 4,273,481 issued June 16, 1981 to John E. Corley et al.
A relatively successful variable dwell control attachment with depth control was invented by Harold R. Ziegelmeyer and described in U.S. Pat. No. 3,762,827 which issued on Oct. 2, 1973. In this device, a sensing sleeve encircles the spindle that drives the drill bit, and the drill bit is capable of telescoping through the sensing sleeve. The spindle driving the drill bit carries on its lower end, an adjustable stop sleeve. The stop sleeve is engageable with the upper end of the sensing sleeve to limit the travel of the spindle and the drill bit. Adjustment of the drilling depth is obtained by positioning the stop sleeve that is threaded on the spindle, by simple rotation of the sleeve relative to the spindle. This device is very simple and generally accurate. It is difficult to obtain precise adjustment since there is no positive means for knowing how far the stop sleeve is rotated relative to the spindle.
An improvement to the device disclosed in U.S. Pat. No. 3,762,827 was the subject of U.S. patent application Ser. No. 533,719, filed 09/19/83, invented by Paul A. Biek and assigned to the assignee of this application. This invention is an improvement to the device disclosed in application Ser. No. 533,719.
In a device constructed in accordance with the teaching of the above application, the depth of drilling is controlled when the end surface on an adjusting sleeve strikes the end surface on a sensing sleeve which has its other end in engagement with the surface of the work piece. The sensing sleeve does not rotate. The adjusting sleeve may rotate and most likely will due to friction between the sensing sleeve and the drive shaft or spindle, the presence of lubricants therein, and vibration which may occur in the tool. If the end surfaces that engage to limit the depth of the drilling are maintained precisely parallel, and then depth of all drilling for each operation would be precisely the same. However, it is virtually impossible to maintain precise parallel surfaces between the parts. If one point on the sensing sleeve is low due, for example, to the sensing sleeve being cocked by the adjusting threads, a low point thereon may engage the end surface of the sensing sleeve at any point on its circumference due to the rotation of the sensing sleeve. Since the end surface of the sensing sleeve may also be disposed at some slight angle relative to the axis of the drill, the depth will vary in accordance with where the engagement occurs between the two end surfaces. While this depth change may be very slight, it does prevent the maintenance of the precise settings for the drilling depth, which will not remain the same from hole to hole.
An object of this invention is to provide an improved dwell and depth attachment for power drills or the like that can be adjusted to provide precise settings for drilling depth and one that will accurately maintain the desired drilling depth.